Berwyn Viaduct Progress - part one (19/01/2002)

excavations excavations

Llangollen Railway Civil Engineer Steve Jones writes ...

Our contractors George Law Ltd of Kidderminster have now completed all excavation works on the Viaduct. The presence of cement concrete rubble haunching between the arches, part of the original design, has meant that the contractor has not had to dig out as much material as originally planned.

This was completed last Friday, and due to the weather having been favourable to expedite his works, he is now ahead of his programme. Drilling and installing of drainage pipes through the arches commences tomorrow, together with scaffolding, and cleaning up of the arch surfaces ready to start receiving the new concrete saddles the following week.

At present, all track, ballast, fill, and other material has been completely removed off the structure, so that the top surfaces of the arches are all fully exposed. The structure is now drying out successfully, and the elevations have actually changed colour, being less black and now more of a light sandstone colour as the moisture within dries out. I walked across the backs of the arches yesterday, and its quite odd crossing over the structure at about 5-6 feet below rail level.

The arch backs all look good, but the original 1860's asphalt waterproofing is life expired and has broken up or completely disintegrated in places, especially over the tops of the arches. The side walls look poor, have separated from the main body of the arches in several places, and exhibit distortion generally, whilst some areas lean out by as much as 6-8". The worst location is on the A5 side over arches 1 and 2, where a 3-4" gap is visible at the foot of the wall through which a steel bar can be quite easilly threaded. Similar, though lesser gaps of up to 2" width are also evident on the same side over arches 4 and 5, and on the river side over arches 3 and 4.

Some things have been discovered during excavation:


Photos by Colin Keyse


Berwyn Viaduct Progress - part two (04/02/2002)

Llangollen Railway Civil Engineer Steve Jones writes ...

Our contractor George Law is now five days ahead of his schedule, and is hoping that if the weather holds out we may be able to get our track back down up to 3 weeks before our intended 23rd March train service start date.

Scaffolding

scaffolding   scaffolding

Above: Scaffolding in progress. The awkwardness of the scaffolding job can be seen.

Conventional scaffolding is now in place around and under arches 1 and 2. I have been on the scaffold under these arches, and can confirm that near to the arch edges the cracks and separation in the brickwork are up to 3 inches wide. Whilst the bodies of the arches under the track are pretty good on the whole, a width of up to 2ft directly under the parapets near to each elevation is very bad throughout. On the river side it is actually possible to pull bricks out of the arch barrel, and in doing so, if one brick is moved at least five or six adjacent ones begin to slide out!

These areas have been very badly damaged by tree root growth, and will have to be completely dismantled and rebuilt. Contractors George Law Ltd are to construct a temporary curved centering in these areas on which to strip out and reconstruct up to a 2ft width of arch edge before it can then be anchored back into the more sound structure under the track. The other arches look similar, if not worse, and the exact extent of works will be determined when scaffolding is complete. However, this problem has been identified and adequately allowed for in the tender prices.

The Rivers Authority have refused to let us build a scaffold from ground level in the area of arches 3, 4, and 5 (over the stream) due to the risk of it being swept away by flood waters. Consequently, it is now agreed that an alternative design of suspended hung scaffold shall be devised which will be supported from a series of novel / totally unique overhead catenary gantries. This will be constructed at normal train loading gauge clearances over the track right across arches 3,4, and 5. This will enable the hanging of a birdcage temporary deck under these arches to permit close hand access for drilling, anchoring, and repointing works.

Progress

on the viaduct

Above: The arches with the first stage of the concrete saddles poured on. The original brickwork can be seen over the piers (between the concrete saddles). The space along the left-hand side is for the reinforced concrete ground beam to support the platform extension.

As regards general progress, all the arches have now been convered over with concrete saddles. This was done by pumping the concrete into place from a convoy of ready mix trucks arriving each day during most of last week.

Work is progressing well on the fixing of the reinforcement steel cages for the platform foundation beam and concreting of the whole length of this is planned for tomorrow - Wednesday.

All new drainage outlets have been installed and are working effectively.

Painting on of the 3 coat bitumen waterproof coating will commence over the whole of the viaduct later this week, weather permitting, and will take 3 working days to complete.

Backfilling of the arches for up to 18 inches thickness will commence later next week, using new 'imported' clean stone. A filter sheeting material will then be laid over this before the remaining depth of the arches will be filled up to track formation level with the best, sandiest / grittyest of the original fill material dug out.

Repointing works to the external stonework of the viaduct has now commenced on the A5 side of arches 1 and 2. A mortar colour and finish type has been agreed between the consultine engineer Jonathan Symonds and myself, and approved by Denbighshire's Listed Building Conservation Officer. The 'Bucket Handle' finish will match the May 1935 repointing works - which according to my records (found at work!) is the last time anything significant was done to the structure appart from removing the platform.

overview

Above: General view looking West showing the overall scale of the job. The sheeting covers material excavated from over the viaduct arches to keep it dry until it is replaced over the concrete saddles being cast over the arches.

Drilling and anchor stitching works will commence under arches 1 and 2 later this week; the stainless steel 'Cintec' anchors arrived on site yesterday afternoon. A specialist subcontractor, John H. Mason Ltd., will carry out this part of the works.

Steelwork for the platform support brackets is currently being fabricated by a firm in Wrexham, whilst the concrete deck units for the platform are to be made over the next two weeks by Cannock Concrete Products Ltd.

end of the line

Above: General view looking towards Llangollen from Berwyn station platform. The temporary buffer stop will be the limit of operations until the track is reinstated on the viaduct. The mound of material excavated from the viaduct includes large concrete blocks which are part of the apparent 'tank trap' described in the previous update. The major component of this however remains in place, serving as a very useful temporary wall to retain the ballast under the track adjacent to the viaduct.

Finally, a sufficient quantity of timber sleepers has now been sourced around the railway to enable the whole stretch of line through Berwyn Station to be relaid in timber, helping to create a realistic pre-war / pre-grouping image for the station to match the paint scheme.